Legumes are important foodstuffs and are likely to become more so in the future. For example, many legumes, especially those in some of the legume genuses, such as Phaseolus, Soja and Lens, are high in protein and provide an inexpensive alternative to animal protein.
Unfortunately, ingestion of some of the most nutritious and abundant legumes can be accompanied by severe flatulence as well as abdominal distress and poor digestibility. More specifically, the flatulence results in discomfort, diarrhea, loss of appetite, and poor growth, all of which have prevented the wide-scale use of these vegetable nutrients.
It is believed that the flatulence is attributable in part to the indigestibility by mammalian digestive enzymes of the flatulence-causing alpha oligosaccharides, such as raffinose, stachyose, and verbascose, and the like, present in legume products. The generally accepted explanation of the action of the alpha oligosaccharides in producing flatulence is that the enzyme alpha galactosidase, which hydrolyzes the .alpha.-oligosaccharides, is not present in the intestinal tract of mammals. Thus, these compounds are not hydrolyzed and dissolved in the digestive tract so that they can be absorbed. Instead, they reach the lower intestine essentially intact. Here, anaerobic bacteria ferment these sugars with the resultant production of carbon dioxide, hydrogen, and methane gases, thereby producing flatus.
Various solutions have been proposed to remove the oligosaccharides from legumes. More specifically, many proposed solutions relate to the use of enzymes to enhance the digestibility of the oligosaccharides. Thus, one solution is to add oligosaccharide-digesting enzymes to the legume itself or as a food supplement to be ingested substantially simultaneously with the ingestion of the legume. For example, U.S. Pat. No. 3,632,646 to Sherba discloses the addition to foodstuff, such as legumes, of .alpha.-galactosidases or other enzyme preparations capable of hydrolyzing the 1,6-linkages of stachyose and other food containing flatulence-causing polysaccharides. U.S. Pat. Nos. 4,376,127 and 4,376,128 to Lunde disclose a process of improving the digestibility of legumes and reducing the flatulence thereof by adding an enzyme system found in pineapple and papaya to the legumes prior to cooking said legumes. U.S. Pat. No. 5,651,967 to Rohde, Jr., et al. discloses a food supplement comprising a beta-fructofuranosidase which is alleged to enhance the digestibility of sugars and reduce flatulence. U.S. Pat. Nos. 5,445,957 and 5,651,967 disclose a food supplement to be ingested simultaneously with the legume comprising a beta-fructofurnanosidase enzyme, a cellulose enzyme and a hemicellulose enzyme which together alleviate gastrointestinal distress caused from the digestion of legumes.
Another solution is leaching the oligosaccharides from the legumes. For example, one method is to soak the legume product in water. Sometimes, the soak is in hot water that gradually cools as the soaking progresses. The soaking water may or may not be changed with fresh water. By this method, it has been found that soaking significantly decreases the .alpha.-galactoside content in lentils. (See, Frias, et al, Journal of Food Protection, 1995, 58, 692-695.) In addition, it has been found that cooking, by either boiling or pressure cooking, also decreases the .alpha.-galactoside content. (See, Vidal-Valverde, et al., Journal of American Dietetic Association, 1993, 93, 547-550).
Industrial soaking, which can be used to leach the oligosaccharides from the legumes, falls into two main processes. The most practiced is an ambient or initially warm soak that is allowed to cool naturally for several hours, followed by a very short blanch at typically 180.degree. F. The high controlled temperature blanch is used to optimize initial rehydration, deaerate the legumes and coagulate the protein to prevent starch leaching out of the legumes during cooking.
A second industrial process is to use multiple short soak times at temperatures sufficient to accelerate the rehydration process. In this process, the legumes are heated in a series of blanchers.
In the Ph.D. thesis of Matrid King from the University of Arkansas (1987), the use of endogenous .alpha.-galactosidase in cowpeas was explored for the purpose of removing the flatulence-causing oligosaccharides therefrom. For example, soaking, germination, and fermentative and non-fermentative incubation treatments for stimulating .alpha.-galactosidase hydrolysis of the oligosaccharides were investigated. The thesis disclosed that the enzyme activity of the .alpha.-galactosidase increased until a temperature maximum of 113.degree. F. was obtained, i.e., above this temperature the enzyme activity decreased. For example, a two minute incubation at 50.degree. C. (122.degree. F.), 55.degree. C. (129.degree. F.) and 60.degree. C. (140.degree. F.) resulted in a 50, 70 and 90% loss of activity compared to the activity at 113.degree. F. In addition, King disclosed that endogenous .alpha.-galactosidase has maximum enzymatic activity at a pH ranging between 4.0 and 5.0.
However, no one heretofore suggested utilizing both leaching action and enzymatic hydrolysis to remove these flatulence causing sugars from legumes. Moreover, no one heretofore suggested removing the sugars at neutral or slightly basic conditions or at temperatures greater than 125.degree. F. Moreover, heretofore, no one had found a method of removing substantially all of the flatulence-causing oligosaccharides from the legumes.
The present inventors have found such a solution. More specifically, they have found a means of significantly removing the flatulence causing oligosaccharides found in legumes.